Under current rules, I don't believe a candidate can give his pledged delegates to another candidate on the first ballot. When it gets to the second or subsequent ballots, trading can be done but only among candidates whose name is in nomination.
The delegates are bound to the candidate, but the candidate can release them from their oath. If Cruz did so with the desire they vote for Trump, some might not, but considering Trump will be within a couple of hundred of the 1,237 goal and Cruz will have 800+, releasing them would give Trump the easy win on the first ballot.